swift234

Prefer compiler-provided conformances  to those required by other protocols.

Previously, we'd warn on this code:

  enum Suit { case Spades, Hearts, Clubs, Diamonds }
  extension Suit : Comparable {}
  func <(...) {...}

because both Comparable and the synthesized conformance to Hashable imply
a conformance to Equatable. However, that's silly: Suit already has a
synthesized conformance to Equatable associated with the main 'enum'
declaration, not the extension. These compiler-provided conformances are
part of the language and something people rely on, so rank them higher than
conformances implied by conforming to a refined protocol.

rdar://problem/21007417

Swift SVN r28849